Roll Observatory packages and add a roll script

packages/observe/benchmark/observable_list_benchmark.dart

+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+library observe.test.benchmark.observable_list_benchmark;
+
+import 'package:observe/observe.dart';
+import 'observation_benchmark_base.dart';
+
+class ObservableListBenchmark extends ObservationBenchmarkBase {
+  final int elementCount = 100;
+
+  ObservableListBenchmark(int objectCount, int mutationCount, String config)
+      : super('ObservableListBenchmark:$objectCount:$mutationCount:$config',
+          objectCount, mutationCount, config);
+
+  @override
+  int mutateObject(ObservableList obj) {
+    switch (config) {
+      case 'update':
+        var size = (elementCount / 10).floor();
+        for (var j = 0; j < size; j++) {
+          obj[j * size]++;
+        }
+        return size;
+
+      case 'splice':
+        var size = (elementCount / 5).floor();
+        // No splice equivalent in List, so we hardcode it.
+        var removed = obj.sublist(size, size * 2);
+        obj.removeRange(size, size * 2);
+        obj.insertAll(size * 2, removed);
+        return size * 2;
+
+      case 'push/pop':
+        var val = obj.removeLast();
+        obj.add(val + 1);
+        return 2;
+
+      case 'shift/unshift':
+        var val = obj.removeAt(0);
+        obj.insert(0, val + 1);
+        return 2;
+
+      default:
+        throw new ArgumentError(
+            'Invalid config for ObservableListBenchmark: $config');
+    }
+  }
+
+  @override
+  ObservableList newObject() {
+    var list = new ObservableList();
+    for (int i = 0; i < elementCount; i++) {
+      list.add(i);
+    }
+    return list;
+  }
+}